This invention relates generally to a screening apparatus for separating solid materials by size. More particularly, this invention pertains to an improved grizzly screen apparatus for separating rocks, concrete, asphalt and other objects by size.
A separation apparatus known as a "grizzly" or "grizzly screen" has been known for many years. Such screens comprise a series of strong, parallel, spaced apart bars that are used to separate large rocks and other debris from material of smaller size. Such screens provide a relatively coarse size separation and are typically used to separate oversize rocks from smaller materials, such as in a gravel plant, a road construction project or quarry.
Typically, a grizzly screen will utilize parallel steel bars which are in a fixed position relative to each other and be spaced about 4-6 inches apart. Thus, the grizzly apparatus will separate rocks and other materials having a dimension greater than the bar spacing from smaller sized materials passing through the screen.
As unsorted debris is dropped onto the screen, objects which are smaller than the bar spacing slip between the bars into a receiving bin, flume, truck or conveyer. Objects larger than the bar spacing cannot slip between the bars arid will roll and/or slide to the lower end of the screen and fall therefrom. The plane of the grizzly bars may vary depending upon the application, but is typically at an angle of about 20 degrees to encourage such rolling and sliding of the larger objects.
A major problem with grizzly screens is that objects having at least one dimension only slightly larger than the bar spacing tend to become jammed between the bars of the screen. These obstructions prevent or retard the discharge of subsequently encountered objects, and the screening capacity increasingly deteriorates. Often such jammed objects require manual removal from the screen using a crowbar, sledge hammer and the like.
It is known to manufacture a grizzly screen whose bars have tapered cross-sections wherein the bottom of each bar is narrower than the top, thus increasing the likelihood that objects passing downward through the screen will not become jammed between the bars. This innovation does not, however, prevent all jamming of the screen and serious jamming problems still occur.
It is desirable to reduce the amount of manual contact which an operator must devote to the removal of jammed obstructions from the grizzly screen. Typically each removal effort requires the operator to remove four to six inch or larger rock from the bars with a heavy crowbar or sledge hammer, and any reduction of such manual clearing work decreases the risk of accident or injury. In addition, some materials sorted by the screen may be of a toxic nature, and it is desirable to reduce manual handling of and close operator exposure to such materials as much as possible.
Still a further shortcoming of existing grizzly screens is that the bars forming such screen are usually rigidly connected to the screen frame and require considerable effort and tools to remove or replace damaged or worn bars. It is desirable to provide a positive attachment apparatus for the screen bars which also allows easy removal and replacement of the bars without tools.
An object of the invention is an improved grizzly screening apparatus which effectively provides for rapid and easy removal of oversize materials which become jammed between the grizzly bars and obstruct the screen.
An additional object of the invention is a grizzly screening apparatus which has a reduced down time for dislodging obstructions from the screen.
A further object of this invention is a grizzly screening apparatus having a controllable movement whereby obstructions may be freed without manual intervention with tools.
Another object of the invention is a grizzly screening apparatus in which obstructing objects may be removed without significantly changing the separation or tolerance characteristic of the screen.
Another object of the invention is a grizzly screening apparatus in which worn or bent bars may be easily and quickly replaced with minimal use of tools.